In the related art, techniques are known in which sheets discharged onto a discharge tray are caused to abut against a predetermined contact hoard using an alignment roller, and are aligned at an end portion on a downstream side in a sheet transport direction with bundles of sheets that are discharged into the discharge tray. In this case, in order to align sheets of a predetermined size, it is necessary to provide a regulation board at a position that matches the sheet size, and a problem arises in that it is not possible to mix sheets of differing sizes in a single tray. In addition, when sheets with sizes that differ greatly from one another (for example, A3 size and postcard size) are discharged, it is difficult to align sheets of various sizes via abutment thereof against the same contact board with a single alignment roller.